The invention relates to a device and a method for fitting motor vehicle tires on rims of disk wheels having the features of the preamble of patent claims 1 and 14.
In such an automatic tire mounting and inflating system, the mounting tool is mounted, for example in the form of two tire fitting rollers and a tire guide roller on a single-armed fitting head. The radial and axial spacing of the fitting head can be adjusted as a function of the type of motor vehicle tire and is embodied so that it can be lowered into a working position. The fitting tool can be composed here of two tire fitting rollers and a tire guide roller. Using an electric motor, the tire fitting tool is turned on the single-armed fitting head about an axis (360xc2x0 rotational movement), permitting fitting to be carried out at a distance from the disk wheel.
Using an electronic torque sensor, a control of the fitting procedure and a display on a pointer instrument are obtained. By means of a light display, upward transgression of a preset maximum permissible torque can be indicated so that a further control can be provided on the mounted tire after such a fitting procedure.
In addition, DE 28 29 935 A1 discloses a device for fitting motor vehicle tires onto rims of disk wheels in which tire fitting tools which can rotate about an axis and are mounted at a distance from the axis are provided, said tire fitting tools being driven and rotated about the respective disk wheel axis during the fitting procedure by means of a drive.
DE 40 28 080 C2 discloses a device and a method of the type mentioned at the beginning, a power supply device being connected to a torque limiting device which, when a predefined torque (torque threshold value) transmitted to the tire fitting tool by the drive motor is exceeded, causes a braking current for stopping the rotational drive to be supplied to the drive motor. A desired torque limitation and thus the objective of achieving gentle handling of the tire during the fitting operation is achieved by supplying power to the drive with torque monitoring. When a preselected drive torque is exceeded as limiting value, the drive brakes in order to avoid damaging the tire.
In the aforesaid limiting value method, the actual switch-off torque is determined by the braking time which is difficult to control, and which is thus an essential determining factor in the damage to the tire. This leads to the problem that the tire itself can still be damaged owing to the braking time even when the fitting procedure is interrupted.
An object of the present invention is therefore to provide a device and a method of the type mentioned at the beginning by means of which more gentle handling of the tire can be ensured.
This object is achieved by means of the measures disclosed in patent claims 1 and 14.
In the invention, the gradient of the torque profile is used as switch-off criterion so that switching off can be achieved significantly before the limiting value of the torque or of the motor current is reached. As a result, the tire is handled more gently and it is ensured that the tire is not damaged by the interrupted fitting procedure. The problem of the braking time which is difficult to control in the limiting value method can thus be avoided.
The power supply device can preferably have a current-conducting device and a torque controller, via which the supply current is supplied to the drive motor, and the gradient-limiting device can be connected to the torque controller in such a way that, when the predefined gradient is exceeded, the controlled variable supplied to the torque controller for the set point torque is set to zero. As a result, simple switching off by means of the set point torque is possible.
In order to improve the starting torque and braking torque, the device can be configured in such a way that when the drive motor is accelerated, an additional electrical reference current is fed to the controller via a closed switching device in the current-conducting device, the signal which corresponds to the set point rotational speed of the drive motor being fed, as controlled variable, to the controller; that, when the set point rotational speed is reached or at the set point rotational speed the switching device in the current-conducting device which supplies the reference variable is opened; and in that when braking occurs the signal which is fed as controlled variable to the torque controller and is proportional to the set point rotational speed is set to zero and the additional reference current is fed to the controller by closing the switching device in the power supply device. An increased reference current is thus supplied during starting up and during braking of the drive.
The gradient-limiting device can have a calculation device for determining the gradient of the torque profile by means of differential quotient formation. Here, a rotational angle signal generator can be provided for sensing the rotational angle of the fitting tool about the axis, the differential quotient being formed with respect to the sensed rotational angle.
As an alternative exemplary embodiment, the calculation device can be configured to form the differential quotient with respect to time. The differential quotient can be carried out by means of torque values and rotational angle values or time values stored in a data store. The output signal of a rotational speed measuring device or the current supplied to the drive motor can be used as torque value. In order to improve the reliability, upward transgression of the predefined gradient for a predetermined percentage of the discretized values stored in the data memory can be used as switch-off criterion in the gradient-limiting device. As a result, switching off can be avoided when there are noncritical brief increases in the gradient.
The gradient-limiting device is preferably configured to determine the gradient in predetermined observation intervals. As a result of this measure, switching off can be avoided when the gradient increases which are non-damaging for the tires and which occur, for example, when the fitting tool is started or when there is first contact with the tire. The observation intervals can be selected on a wheel-specific basis.
The invention consequently provides a protection device by means of which more gentle handling of the tire during the fitting procedure is achieved and thus damage owing to the braking time is prevented.